Electrical resistivity of Si3N4-SiC-MeSi2 (Me = Nb, Mo, W, Zr) composites

Si3N4-SiC and Si3N4-SiC-MeSi2 (Me = Nb, Mo, W, Zr) composites were densified by means of hot pressing at 1840 °C. Additional heat treatment was performed at 1900 °C in a gas pressure furnace at 1900 °C. The hot-pressed and heat-treated composites were investigated with X-ray diffraction, scanning electron microscopy and measurements of their electrical resistivity. The electrical resistivity of the hot-pressed Si3N4-SiC composite was about 104 Ocm. The addition of silicides yielded a decrease in composite resistivity to values of about 101-10-2 Ocm. The subsequent heat treatment results in a further decrease of the resistivity by at least one order of magnitude for all composites. An a RT v transformation in SiC was detected in the Si3N4-SiC-MeSi2 composites with XRD and electron backscatter diffraction (EBSD) analysis. The a RT v transformation in SiC was strongly associated with a high-nitrogen doping concentration of the SiC grains, resulting in lower electrical resistivity of the Si3N4-SiC-MeSi2 composites in comparison with the Si3N4-SiC composite. Differences in the solution-precipitation process of SiC have been claimed as a reason for the highly doped SiC grains in the Si3N4-SiC-MeSi2 composites.